This invention relates to a circuit breaker in which pressure in a container of the breaker is suppressed. The circuit breaker in this invention generates an arc in a container, normally a small-sized container such as a circuit breaker, a current limiter or an electromagnetic switch.
A prior art circuit breaker will be described below.
FIGS. 1A, 1B and 1C are sectional views showing a conventional circuit breaker in different operating states.
Numeral 1 designates a cover, and numeral 2 a base, which forms an insulating container 3 with the cover 2. Numeral 4 designates a stationary contactor, which has a stationary conductor 5 and a stationary contact 6 at one end of the conductor 5, and the other end of the conductor 5 becomes a terminal connected to an external conductor (not shown). Numeral 7 designates a movable contactor, which has a movable conductor 8 and a movable contact 9 disposed oppositely to the contact 6 at one end of the conductor 8. Numeral 10 designates a movable contactor unit, and numeral 11 a movable element arm, which is attached to a crossbar 12 so that each pole simultaneously opens or closes. Numeral 13 designates an arc extinguishing chamber in which arc extinguishing plates 14 are retained by side plates 15. Numeral 16 designates a toggle linkage, which has an upper link 17 and a lower link 18. The link 17 is connected at one end thereof to a cradle 19 through a shaft 20 at the other end thereof to one end of the link 18 through a shaft 21. The other end of the link 18 is connected to the arm 11 of the contactor unit 10. Numeral 22 designates a tiltable operating handle, and numeral 23 an operating spring, which is provided between the shaft 21 of the linkage 16 and the handle 22. Numerals 24 and 25 respectively designate a thermal tripping mechanism and an electromagnetic tripping mechanism, which are respectively provided to rotate a trip bar 28 counterclockwise via a bimetal 26 and a movable core 27. Numeral 29 designates a latch, which is engaged at one end thereof with the bar 28 and at the other end thereof with the cradle 19.
When the handle 22 is tilted down to the closing position in the state that the cradle 19 is engaged with the latch 29, the linkage 16 extends, so that the shaft 21 is engaged with the cradle 19, with the result that the contact 9 is brought into contact with the contact 6. This state is shown in FIG. 1A. When the handle 22 is then tilted down to the open position, the linkage 16 is bent to isolate the contact 9 from the contact 6, and the arm 11 is engaged with a cradle shaft 30. This state is shown in FIG. 1B. When an overcurrent flows in the circuit with the contacts in the closed state shown in FIG. 1A, the mechanism 24 or 25 operates, the engagement of the cradle 19 with the latch 29 is ended, the cradle 19 rotates clockwise around the shaft 30 as a center, and is abutted against a stop shaft 31. Since the connecting point of the cradle 19 and the link 17 is past the operating line of the spring 23, the linkage 16 is bent by the elastic force of the spring 23, each pole automatically cooperatively breaks the circuit via the bar 12. This state is shown in FIG. 1C.
The behavior of an arc which is generated when the circuit breaker breaks the current will be described below.
When the contact 9 is contacted with the contact 6, the electric power is supplied sequentially from a power supply side through the conductor 5, the contacts 6 and 9 and the conductor 8 to a load side. When a large current such as a shortcircuiting current flows in this circuit in this state, the contact 9 is separated from the contact 6 as described before. In this case, an arc 32 is generated between the contacts 6 and 9, and an arc voltage is produced between the contacts 6 and 9. Since this arc voltage rises as the distance from the contact 6 to the contact 9 increases and the arc 32 is urged by the magnetic force toward the plate 14 so as to be extended, the arc voltage is further raised. In this manner, an arc current approaches the current zero point, thereby extinguishing the arc to complete the breakage of the arc. The huge injected arc energy eventually becomes thermal energy, and is thus dissipated completely out of the container, but transiently raises the gas temperature in the limited space in the container and accordingly causes an abrupt increase in the gas pressure. This causes a deterioration in the insulation in the circuit breaker and an increase in the quantity of discharging spark escaping from the breaker, and it is thereby feared that an accident such as a power source shortcircuit or damage to the circuit breaker body will occur.